1. Field of the Invention
The present invention relates to a position detection apparatus, a drive control apparatus, and a lens apparatus.
2. Description of the Related Art
A so-called absolute position detection unit such as a potentiometer and a so-called relative position detection unit such as an optical system incremental type rotary encoder are proposed for a lens position detection unit of an image pickup apparatus in general.
An absolute type rotary encoder (hereinafter, which will be referred to as “absolute encoder”) is used for an absolute position detection unit. The absolute encoder can uniquely detect a position of a position detection target. In a case where the absolute encoder is used for the lens position detection unit, the absolute position can be found out immediately after power-on, and also the position detection can be carried out at a high accuracy.
A vernier type absolute encoder is used for the absolute encoder (see Japanese Patent Laid-Open No. 8-304113). The vernier type absolute encoder includes a main track and at least one sub track, and the main track and the sub track are composed of grating patterns. Slit pitches of the grating patterns constituting the main track and the sub track are different from each other. The vernier type absolute encoder is an encoder configured to set a section where a fine deviation of detection signals caused by a difference in the slit pitches between these respective tracks circulates once as an absolute position (absolute positioning).
The following problem occurs in a case where the vernier type absolute encoder (absolute position detection unit) disclosed in Japanese Patent Laid-Open No. 8-304113 is used as the lens position detection unit.
At the time of the power-on of the image pickup apparatus, signals of the plurality of tracks of the vernier type absolute encoder are read out at the same time and combined with each other to calculate the absolute position. However, when a lens or an operation ring corresponding to the position detection target is moved at the time of the power-on of the image pickup apparatus, a temporal lag is caused in timings for A/D conversion in a system where the signals read out from the plurality of tracks are sequentially subjected to the A/D conversion. As a result, a problem occurs that a signal synchronism is not secured, and an accurate position detection is not carried out.
To solve the above-mentioned problem, it is conceivable to use the relative position detection unit such as the optical system incremental type rotary encoder instead of the absolute position detection unit for the lens position detection unit of the image pickup apparatus. Although the incremental type rotary encoder has an advantage that the position can be detection at a higher accuracy as compared with the potentiometer, the incremental type rotary encoder also has a disadvantage that zero return for identifying a reference position is to be carried out at the time of the power-on or at the time of the recovery from an emergency stopped state.